Guidance devices are used in countless numbers in order to guide pointed fasteners, such as, for example, drive pins and threaded studs, as such fasteners are driven by means of powder-actuated tools. Typically, a drive pin has an elongate shank, which is formed with a pointed end, and a head, which when viewed axially is circular. The shank may be somewhat flared where the shank merges with the head.
Typically, a threaded stud has an unthreaded portion, which resembles the shank of a drive pin and which has a pointed end, and a threaded portion which extends axially from the unthreaded portion, resembles the threaded shank of a machine screw, and which has a blunt end. The blunt end, which is opposite to the pointed end, may be partially unthreaded.
Typically, a powder-actuated tool, as mentioned above, has a muzzle bushing, from which such a fastener is driven, and a driver, which when driven axially through the muzzle bushing impacts and drives the fastener. The muzzle bushing, which has a circular bore, may alternatively be known as a barrel extension. Typically, the circular bore of themuzzle bushings has a bore diameter ranging from approximately 0.300 inch (7.62 mm) to approximately 0.354 inch (9.00 mm) and a bore length exceeding 3.0 inch (7.62 cm). A commercial source for such powder-actuated tools is ITW Ramset-Red Head (a division of Illinois Tool Works Inc.) of Wood Dale, Illinois.
It is known to assemble a guidance device upon each fastener before the fastener is inserted into the muzzle bushing of such a tool. In many instances, the guidance device is used not only to guide the fastener but also to retain the fastener within the muzzle bushing before the fastener is driven, whereby the fastener is retained within the muzzle bushing even if the muzzle bushing is placed in a vertical orientation.
If such a fastener were to be forcibly driven into a workpiece, such as, for example, a piece of structural steel, or into a substrate, such as a substrate of concrete or masonry, at an angle deviating significantly from a right angle, the utility of the fastener would be significantly diminished. Moreover, the fastener could bend, or break. It is important, therefore, for such a fastener to be concentrically guided within the muzzle bushing of such a tool.
A guidance device of a known type constituting prior art vis-a-vis this invention and enjoying wide acceptance among contractors and other users, is disclosed in U.S. Pat. No. 4,286,496 issued to Harris. As disclosed therein, the guidance device is made from an elastomeric material, which has a hardness of 65 to 75 durometers on the Shore A scale. Such device has what is described therein as an axially elongate, hollow, cylindrical body portion, upon the outer surface of which are formed a plurality of flexible, axially elongate fins (or fin members) extending radially at regular circumferential intervals. Alternating ones of the fins (or fin members) are described therein as being of substantially greater radial extent than the adjacent ones. Such device is described therein as being useful in connection with a range of sizes of muzzle bushing bores. The shorter fins are described therein as acting to prevent the fastener point from being deflected off-center by more than half the difference between the bore diameter and the circumscribed diameter defined by means of the shorter fins.
The guidance device described as prior art in such Harris patent has a tubular body and three integral, radial ribs, of equal length when measured radially.
A guidance device such as the guidance device disclosed in such Harris patent may alternatively be known, in view of the fluted shape of such device, as a guidance flute, a term employed herein.
A guidance device of a different type constituting prior art vis-a-vis the present invention is used to protect the starting threads of a threaded stud and to guide the stud within a muzzle bushing as the stud is driven. Such a device fits snugly over the starting threads but allows the blunt end of the stud to remain exposed where such end is to be later impacted by means of the tool driver. Such a device alternatively be known, in view of its usage, as a guidance tip, a term employed herein.
It is known, moreover, to employ a guidance device of each of the aforesaid type on a threaded stud, namely, a guidance flute on the unthreaded portion of such stud and a guidance tip on the blunt end of such stud.
Herein, all references to driving a pointed fastener, such as, for example, a drive pin or a threaded stud, into masonry are meant to refer to driving such a fastener into a grout-filled concrete block or the like, not into a hollow concrete block, common brick, or the like.
Although guidance devices constituting prior art, as described above, have proved to be generally satisfactory, there has remained a need, to which this invention is addressed, for improved guidance devices enabling pointed fasteners, such as, for example, drive pins and threaded studs, to be concentrically guided within different muzzle bushings which may exhibit a range of muzzle bushing diameters. The need has embraced both guidance flutes and guidance tips.